Emerging observations indicate that the processes of cardiomyocyte growth and cardiac angiogenesis must remain balanced throughout life and suggest that excess cardiac hypertrophy and/or insufficient cardiac angiogenesis in response to stress leads to impaired cardiac function, cardiomyopathy, and heart failure. An imbalance between cardiac growth and cardiac angiogenesis may play an essential role in the development and progression of multiple forms of human heart failure. Intriguingly, several recent studies indicate that the cardiomyocyte itself functions in a paracrine fashion to regulate blood vessel growth in the heart in response to stress. However, the molecular regulation of this paracrine function of cardiomyocytes (the angiogenic potential of cardiomyocytes) is not well understood. Our central hypothesis is that under conditions of stress that lead to cardiac hypertrophy, platelet derived growth factor receptor beta (PDGFR-) is an upstream regulator of the angiogenic potential of cardiomyocytes. In support of this hypothesis, we have shown that cardiomyocyte specific Pdgfrb knockout mice exposed to pressure overload stress develop cardiac dysfunction, ventricular dilatation and heart failure, associated with defective coronary microvascular function. These findings demonstrate that PDGFR- signaling is an essential and heretofore unappreciated mediator of the cardiac stress response. To further understand the role of PDGFR- signaling as a regulator of the angiogenic potential of cardiomyocytes, we will determine if cardiomyocyte PDGFR- signaling regulates coronary angiogenesis in response to pathologic stressors that lead to cardiac hypertrophy using a Pdgfrb knockout model and also via administration of anti-cancer agents whose targets include PDGFR- (Aim One). We will further determine if cardiomyocyte PDFGR- signaling is required to promote coronary angiogenesis which accompanies physiologic cardiac growth observed in early postnatal life or in adult life in response to exercise training using a Pdgfrb knockout model (Aim Two). Finally, we will determine the mechanism(s) by which PDGFR- signaling regulates the angiogenic potential of cardiomyocytes using an in vitro model of cultured cardiomyocytes in which PDGFR- is deleted. Confirmation of our overall hypothesis through the experiments proposed in this application would suggest that PDGFR- in the heart may be a novel area of concern in evaluating and treating selected forms of human heart failure, and in addition, may inform strategies to prevent and/or treat cardiotoxicity in cancer patients treated with agents that target PDGFR signaling.